Rain attenuation measurement techniques are studied with appropriate prediction of rain attenuation at Ku-band for Koreasat 6. This is accomplished by the establishment of experimental setup in Mokdong at 12.25 GHz link. The databases are analyzed for three years, 2013 till 2015. During observation period, rainfall rate of 50 mm/hr is obtained which is measured by OTT Parsivel showing the signal attenuated by 10.7 dB for 0.01% of the occurrence. Comparison with the measured data demonstrates that the proposed technique provides sufficiently accurate estimation for Ku-band signal attenuation in site specifically whose effectiveness is performed through the statistical analysis against the established rain attenuation models. The proposed technique is judged through the error matrices where relative error margins of 52.82, 4.11, and 23.64% are obtained for 0.1%, 0.01%, and 0.001% of the occurrence.
Absorption and scattering by rain at frequencies above 10 GHz can result in the reduction of transmitted signal amplitude, which in turn reduce the reliability, availability, and performance of the communication link [
The technique for predicting the rain attenuation of Ku-band satellite signal during rain events has been presented for Mokdong Station. In addition, the established method of study of signal attenuation due to rain is analyzed [
Three methods are crucial for the better estimation of signal attenuation due to rain which can be categorized as the evaluation of specific attenuation [
The ITU-R rain attenuation model [
If
If
Otherwise,
Full rainfall rate distributions are used to analyze the signal attenuation due to rain. The numerical coefficients are obtained by multiple nonlinear regressions, obtained from available ITU-R databanks [
It is based on the log-normal distribution of rain rate and rain attenuation. Even though this method is similar to the ITU-R P. 618-12 [
It was developed to utilize algebraic equations for specific attenuation coefficients, isotherm height, and path profile on earth-space communication links operating in the range from 10 to 35 GHz. This method consists of the relationship between specific attenuation and rain rate, statistics of the point rainfall intensity and spatial distribution of rainfall [
The model depends on the 0°C isotherm height,
It studies the statistics that is based on elevation angle less than 60° [
It features the suitable method for rain attenuation prediction to be used in satellite radio link which is tested over 77 satellite links placed in Europe, the US, Japan, and Australia. The coefficients details necessary for the calculation of rain attenuation are mentioned in [
This model was accepted by the European Space Agency as a suitable model which was designed to enhance the prediction performance at lower probability exceedance levels [
The proposed technique is based on the behavior of signal as it is attenuated towards the direction of communication path between satellite and ground station at 0.01% of occurrence. The two quantities are related as
Rain attenuation of Ku-band beacon signal over an earth-space link has been measured by a receiving signal at frequency 12.25 GHz transmitted with circular polarization from satellite Koreasat 6, situated at 116°E at an elevation angle of 45° since 2013 [
Link description for 12.25 GHz [
Type | Descriptions | Specification |
---|---|---|
System Location | Location | 37.5447°N, 126.8833°E |
Elevation angle | 45° | |
Degree of tilt | 197.5° | |
Low-lying (km) | 0.055 | |
| ||
Receiver Antenna | Prototype | Off-set parabolic |
Operating range | 10.95 ~ 31 | |
Polarization | Circular | |
Gain | 55 dB ± 2 dB | |
Dynamic Range (dB) | 18.3 | |
| ||
Optical Disdrometer | Type | OTT Parsivel |
Measuring area | 54 cm2 | |
Particle size | 0.2 to 25 mm | |
Velocity drop | 0.2 to 20 m/s | |
Rain Intensity | Up to 1200 mm/hr | |
Temperature range | -40°C to +70°C |
The received beacon signal levels are sampled for every 10 seconds and averaged over 1 minute. The rain rates are measured by OTT Parsivel with 99.95% of the validity. OTT Parsivel is the laser based optical disdrometer. The parallel rays between emitter and receiver help to measure the required precipitation characteristics with the change in signal output voltage. This determines the magnitude of drops particle size whereas the interval of original signal helps in determination of the velocity. This determines the required rain rate. The sensor built on the OTT Parsivel conveys messages to computer with the support of RS 485. Heating system obstructs the ice build-up process for every second. Further detail procedures are listed in [
System diagram of experimental setup [
Figure
Variation of 12.25 GHz signal attenuation [
Thus, the required attenuation is calculated as
Distribution of Rain attenuation at Mokdong [
Furthermore, the plot of rainfall rate distribution for various integration times near location of Icheon is presented in [
Distributions of rain attenuation at 12.25 GHz are shown in Figure
Variation of signals against ITU-R P. 618-13 for various integration times [
Rain attenuation versus rain rate [
The proposed method along with the rain attenuation models is studied against the measured result as shown in Figures
Prediction at 12.25 GHz for Mokdong Station [
Prediction at 12.25 GHz for Yong-in Station [
In 12.25 GHz from Figure
Interestingly, CG generates close approximation against the measured rain attenuation when P < 0.01%. It predicts 2.39, 11.05, and 25.84 dB, respectively, at 0.1%, 0.01%, and 0.001% of the time whereas SAM predicts 2.37, 12.52, and 26.2 dB, respectively. DAH, Unified, and GL show underestimation of rain attenuation for all-time percentage, but the closer prediction is obtained by the application of DAH method in low time of occurrence. As seen, DAH, Unified, and GL show 2.66, 8.19, and 17.84 dB; 2.63, 8.42, and 14.55 dB; and 2.09, 8.41, and 13.64 dB, respectively at 0.1%, 0.01%, and 0.001% of the time. Karasawa shows preferable estimation at 0.01% of the time, but greater overestimation and underestimation are observed for lower and higher time percentages, respectively, as compared to other methods. Additionally, RK gives the better estimation for higher time percentage, but overestimation is noted on lower time percentage. Karasawa and RK estimate 3.07, 9.72, and 37.45 dB and 5, 15.79, and 21.48 dB, respectively, at 0.1%, 0.01%, and 0.001% of occurrence. Additionally, effectiveness of methods is analyzed from error analysis.
Prominent methods along with proposed technique are tested in Yong-in Station. Unfortunately, unavailability of sufficient database for all-time percentages has limited the significance of the study. However, data at 0.1 and 0.01% of the time for 2007 as noted from [
Rain attenuation prediction model for Earth-satellite link is determined for exceeding time percentages 0.001% to 1%. Hence, the percentage errors,
Calculated error percentage [0.001% to 1%] for 12.25 GHz.
Procedures | Matrices | Occurrence | ITU-R P.311-15 | ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | 0.5 | 0.3 | 0.2 | 0.1 | 0.05 | 0.03 | 0.02 | 0.01 | 0.005 | 0.003 | 0.002 | 0.001 | | | | ||
ITU-R P. 618-13 | -0.84 | -0.78 | -0.72 | -0.66 | -0.53 | -0.38 | -0.26 | -0.15 | 0.04 | 0.19 | 0.29 | 0.32 | 0.24 | ||||
STD | 0.59 | 0.53 | 0.47 | 0.41 | 0.28 | 0.13 | 0.01 | 0.10 | 0.29 | 0.43 | 0.54 | 0.57 | 0.48 | -0.45 | 0.64 | 0.78 | |
RMS | 4.70 | 4.98 | 4.94 | 4.79 | 4.17 | 3.23 | 2.40 | 1.49 | 0.44 | 2.27 | 3.89 | 4.77 | 4.49 | ||||
| |||||||||||||||||
Unified | -0.94 | -0.88 | -0.84 | -0.79 | -0.67 | -0.51 | -0.42 | -0.34 | -0.21 | -0.15 | -0.11 | -0.14 | -0.23 | ||||
STD | 0.46 | 0.40 | 0.36 | 0.31 | 0.19 | 0.03 | 0.06 | 0.14 | 0.27 | 0.33 | 0.37 | 0.34 | 0.25 | -0.02 | 0.63 | 0.63 | |
RMS | 5.27 | 5.66 | 5.78 | 5.76 | 5.27 | 4.39 | 3.86 | 3.35 | 2.28 | 1.86 | 1.47 | 2.11 | 4.45 | ||||
| |||||||||||||||||
DAH | -0.89 | -0.85 | -0.80 | -0.76 | -0.66 | -0.55 | -0.46 | -0.38 | -0.23 | -0.12 | -0.03 | 0.00 | -0.06 | ||||
STD | 0.44 | 0.40 | 0.35 | 0.31 | 0.22 | 0.10 | 0.02 | 0.06 | 0.21 | 0.33 | 0.41 | 0.44 | 0.39 | -0.76 | 0.66 | 1.01 | |
RMS | 4.98 | 5.41 | 5.52 | 5.53 | 5.24 | 4.73 | 4.30 | 3.75 | 2.51 | 1.46 | 0.45 | 0.06 | 1.16 | ||||
| |||||||||||||||||
SAM | -0.99 | -0.95 | -0.91 | -0.86 | -0.70 | -0.45 | -0.27 | -0.12 | 0.17 | 0.36 | 0.49 | 0.47 | 0.38 | ||||
STD | 0.73 | 0.69 | 0.65 | 0.60 | 0.44 | 0.19 | 0.01 | 0.14 | 0.43 | 0.62 | 0.75 | 0.73 | 0.64 | -0.87 | 1.35 | 1.61 | |
RMS | 5.53 | 6.09 | 6.28 | 6.27 | 5.54 | 3.88 | 2.49 | 1.14 | 1.82 | 4.37 | 6.57 | 6.91 | 7.20 | ||||
| |||||||||||||||||
Crane Global | -0.99 | -0.95 | -0.90 | -0.85 | -0.70 | -0.48 | -0.32 | -0.20 | 0.03 | 0.18 | 0.28 | 0.26 | 0.36 | ||||
STD | 0.66 | 0.62 | 0.57 | 0.52 | 0.37 | 0.15 | 0.01 | 0.13 | 0.36 | 0.51 | 0.61 | 0.59 | 0.69 | -0.9 | 1.26 | 1.55 | |
RMS | 5.52 | 6.05 | 6.22 | 6.19 | 5.51 | 4.11 | 3.01 | 1.94 | 0.35 | 2.16 | 3.72 | 3.80 | 6.84 | ||||
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Ramachandran and Kumar | -0.79 | -0.71 | -0.63 | -0.55 | -0.37 | -0.12 | 0.13 | 0.42 | 0.48 | 0.45 | 0.43 | 0.36 | 0.13 | ||||
STD | 0.73 | 0.65 | 0.57 | 0.49 | 0.31 | 0.06 | 0.19 | 0.47 | 0.54 | 0.51 | 0.49 | 0.42 | 0.19 | -0.21 | 0.62 | 0.65 | |
RMS | 4.43 | 4.56 | 4.34 | 4.01 | 2.90 | 1.00 | 1.25 | 4.07 | 5.09 | 5.48 | 5.69 | 5.28 | 2.48 | ||||
| |||||||||||||||||
Gracia Lopez | -0.99 | -0.95 | -0.91 | -0.87 | -0.74 | -0.55 | -0.44 | -0.35 | -0.21 | -0.16 | -0.13 | -0.17 | -0.28 | ||||
STD | 0.47 | 0.43 | 0.39 | 0.35 | 0.22 | 0.03 | 0.08 | 0.17 | 0.31 | 0.36 | 0.39 | 0.35 | 0.24 | -1.16 | 1.16 | 1.64 | |
RMS | 5.53 | 6.10 | 6.31 | 6.34 | 5.81 | 4.74 | 4.05 | 3.44 | 2.30 | 1.98 | 1.78 | 2.56 | 5.36 | ||||
| |||||||||||||||||
Karasawa | -0.89 | -0.83 | -0.77 | -0.72 | -0.61 | -0.49 | -0.39 | -0.29 | -0.09 | 0.07 | 0.41 | 0.80 | 0.97 | ||||
STD | 0.67 | 0.61 | 0.55 | 0.50 | 0.39 | 0.27 | 0.17 | 0.08 | 0.13 | 0.29 | 0.63 | 1.02 | 1.19 | -0.53 | 0.81 | 0.97 | |
RMS | 4.97 | 5.30 | 5.32 | 5.25 | 4.83 | 4.18 | 3.61 | 2.87 | 0.98 | 0.83 | 5.47 | 11.76 | 18.45 | ||||
| |||||||||||||||||
Proposed | -0.85 | -0.79 | -0.73 | -0.67 | -0.55 | -0.40 | -0.29 | -0.19 | 0.00 | 0.14 | 0.24 | 0.28 | 0.19 | ||||
STD | 0.57 | 0.51 | 0.45 | 0.39 | 0.27 | 0.12 | 0.01 | 0.09 | 0.28 | 0.42 | 0.52 | 0.55 | 0.47 | -0.49 | 0.64 | 0.81 | |
RMS | 4.74 | 5.05 | 5.03 | 4.91 | 4.34 | 3.45 | 2.69 | 1.83 | 0.00 | 1.72 | 3.25 | 4.06 | 3.67 |
Calculated error percentage [0.005% to 0.5%] for 12.25 GHz.
Procedures | Matrices | Occurrence | ITU-R P.311-15 | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
0.5 | 0.2 | 0.1 | 0.05 | 0.02 | 0.01 | 0.005 | | | | ||
ITU-R P. 618-13 | -0.59 | -0.38 | -0.35 | -0.22 | 0.04 | -0.11 | -0.14 | ||||
STD | 0.46 | 0.24 | 0.22 | 0.08 | 0.18 | 0.03 | 0.01 | -0.15 | 0.19 | 0.24 | |
RMS | 1.77 | 1.32 | 1.75 | 1.30 | 0.31 | 1.16 | 2.17 | ||||
| |||||||||||
DAH | -0.66 | -0.48 | -0.46 | -0.34 | -0.12 | -0.24 | -0.27 | ||||
STD | 0.46 | 0.28 | 0.26 | 0.14 | 0.08 | 0.04 | 0.07 | -0.23 | 0.22 | 0.32 | |
RMS | 3.94 | 2.85 | 5.21 | 4.19 | 0.66 | 6.94 | 16.30 | ||||
| |||||||||||
Ramachandran and Kumar | -0.32 | 0.04 | 0.10 | 0.39 | 1.16 | 0.57 | 0.28 | ||||
STD | 0.49 | 0.13 | 0.07 | 0.22 | 0.99 | 0.39 | 0.11 | 0.12 | 0.23 | 0.26 | |
RMS | 0.96 | 0.13 | 0.51 | 2.34 | 8.14 | 6.22 | 4.25 | ||||
| |||||||||||
Karasawa | -0.63 | -0.42 | -0.03 | -0.26 | -0.01 | 0.16 | 0.07 | ||||
STD | 0.55 | 0.33 | 0.06 | 0.18 | 0.08 | 0.25 | 0.16 | -0.1 | 0.24 | 0.26 | |
RMS | 1.90 | 1.45 | 0.13 | 1.58 | 0.07 | 1.77 | 1.08 | ||||
| |||||||||||
Proposed | -0.47 | -0.20 | -0.17 | 0.00 | 0.31 | 0.12 | 0.06 | ||||
STD | 0.44 | 0.17 | 0.14 | 0.02 | 0.34 | 0.14 | 0.09 | -0.03 | 0.17 | 0.17 | |
RMS | 1.41 | 0.70 | 0.85 | 0.03 | 2.20 | 1.29 | 0.91 |
Calculated error percentage over 0.1% and 0.01% of the time.
Methods | Parameters | Time Percentage | ITU-R P.311-15 | |||
---|---|---|---|---|---|---|
0.1 | 0.01 | | | | ||
Unified | -0.09 | -0.14 | -0.11 | 0.04 | 0.12 | |
STD | 0.03 | 0.03 | ||||
RMS | 0.43 | 1.52 | ||||
| ||||||
SAM | 0.07 | 0.36 | 0.18 | 0.12 | 0.22 | |
STD | 0.14 | 0.14 | ||||
RMS | 0.36 | 3.92 | ||||
| ||||||
Crane Global | -0.05 | 0.14 | 0.04 | 0.09 | 0.10 | |
STD | 0.10 | 0.10 | ||||
RMS | 0.26 | 1.51 | ||||
| ||||||
Gracia Lopez | -0.15 | -0.15 | -0.15 | 0.01 | 0.15 | |
STD | 0.00 | 0.00 | ||||
RMS | 0.15 | 0.15 |
As depicted from Table
In contrast, DAH, Unified, and GL models give underestimation against the calculated rain attenuation, but less underestimation is shown by DAH method which signifies its suitability in low time occurrence. In addition, at 0.01%, ITU-R P. 618-13 and the proposed approach seem to provide fairly more accurate results than the other models of interest. To illustrate, ITU-R P. 618-13 results in error percentage of 53%, 4%, and 24% while it is 67%, 21%, 23%; 66%, 23%, 6%; 70%, 17%, 38%; 70%, 3%, 36%; 37%, 48%, 13%; 74%, 21%, 28%; 61%, 9%, 97%; 55%, 0%, 19% for Unified, DAH, SAM, CG, RK, GL, Karasawa, and the proposed approach at 0.1%, 0.01%, and 0.001% of occurrence, respectively. ITU-R P.618-13 and the proposed technique result in fewer values of
Table
Table
Various models are compared to predict rain attenuation at Ku-band over an earth-space path. The propagation impairments for 12.25 GHz satellite communication links in Mokdong Station, along with database provided from Young-in station are studied. The rain rates at 0.01% of the time are 50.35 and 59 mm/hr for two experimental locations, namely, Mokdong and Yong-in Stations. The results show that at higher time percentage when 0.01% ≤ P ≤ 1%, ITU-R P.618-13, Ramachandran and Kumar, proposed approach shows the better estimation of rain attenuation. Conversely, when 0.001% ≤ P ≤ 0.1%, ITU-R P. 618-13, DAH, and the proposed approach show good estimation against the measured results. The predictive capability of the model is judged through the relative error analyses, standard deviation, root mean square values, and ITU-R P. 311-15. Thus, the paper presents comparison of measured data with the existing rain attenuation prediction models and categorizes the best fitting models. Overall, ITU-R P. 618-13 shows better applicability for prediction of rain attenuation until the sufficient database from other locations become available. ITU-R P. 618-13 model shows better estimation and could be used until and unless sufficient dataset of rain attenuation measurement at Ku-band is made available from other location of South Korea. However, as per the rain attenuation and rain rate measurement obtained from two specific locations, the proposed method shows better estimation. This emphasizes the advantages of the proposed approach as compared to existing models.
The empirical result generated would be the helpful tool for system designers to determine the link margin at the specific site. However, additional tests and experimental data are necessary for better understanding of the present line of study for Ku-band satellite communication link. The contribution describes some preliminary steps aiming at devising appropriate methodology for prediction of rain attenuation affecting earth-space communication link.
It could be provided upon request from the reader on the approval from National Radio Research Agency (RRA).
The authors declare that they have no conflicts of interest.
We want to extend our thankfulness towards National Radio Research Agency (RRA) for providing and supporting us with the valuable database of satellite system. Authors also like to thank School of Engineering, Macquarie University, NSW, Australia, for providing the environment to further carry out the research work.